1. Field of the Invention
The present invention relates to a water mixing valve apparatus and, more particularly, to improvements in the control system of a water mixing valve apparatus having a servo controlled mixing valve.
2. Description of the Related Art
Previously it was known to provide an electronically controlled mixing valve for mixing hot and cold water to provide outlet water of a desired temperature. The apparatus was provided with a control loop having a temperature sensor in the outlet of the mixing valve so that the mixing valve could be adjusted to provide a desired outlet temperature. It was also known to provide the mixing valve apparatus as part of a shower, e.g. for washing.
This known mixing valve apparatus has a problem when it is installed in a non-linear environment. For instance, where a mixing valve is installed in a water system having a higher pressure cold water supply, the first part of movement of the mixing valve will have little effect in raising the outlet temperature and the outlet temperature will be very sensitive to movement of the valve in a later small range.
To overcome this problem, it is possible to adapt the mixing valve for a particular pressure system, for instance by inserting restrictors in the inlet pipes. However, the installation of such restrictors is not a trivial matter and, unless the nature of a water system is known in advance, it is necessary to use trial and error to determine the correct restrictor. Furthermore, it is necessary to produce and stock a selection of different restrictors for different types of water system.
It is also possible to use a control loop which adjusts dynamically according to sensed operating conditions. However, this is unduly complicated and requires the control loop to reconfigure itself when the valve is moved between different portions of a stable, but non-linear environment.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the water inlets and outlets being for connection to an external water system;
a valve servo for moving the position of the valve;
a control system for operating the valve servo and thereby controlling at least the temperature at the water outlet; wherein
the control system characterises he external water system in which the mixing valve is connected and optimizes control of the valve according to he characterisation.
In this way, it is not necessary for different mixing valves to be provided for different installations or to provide additional parts to adapt the mixing valve for different installations. The control system can adapt the way it controls the mixing valve according to the properties of the external water system In particular, for a given temperature change at a particular point in the temperature range, the control system can move the mixing valve by a different amount according to how the external water system has been characterised. Where the control system uses an outlet temperature sensor with a control loop, it can optimise control of the valve by varying, according to the characterisation, the amount of movement of the valve to correct a difference between actual and desired temperature as detected by the temperature sensor. In other words, the control loop in effect employs a gain which varies through the valves range according to the characterisation.
However, for the particular characterization, appropriate gains are known for positions throughout the operating range and there is no need for the system to dynamically change the gain on the basis of sensed conditions. A respective characterization represents an entire operating range.
Preferably, the characterisation takes account of at least one of inlet water flows, pressures and temperatures. This enables the mixing valve apparatus to be optimised for a wide variety of external water systems.
The characterisation used by the control system can be selected by the user, for instance by means of an input selector. In this way, the user merely preselects the type of external water system in which the mixing valve apparatus is installed or changes the selection until an optimum response is observed.
On the other hand, the control system could automatically determine the characterisation on the basis of operating conditions of the valve.
In this way, the control system determines the characterisation of the external water system on the basis of the properties of the water at the outlet of the mixing valve compared to the controlled position of the valve to produce those properties.
Hence, the operating conditions may include the mixed temperature at the outlet and the position of the mixing valve. Furthermore, they may include the cold water inlet temperature or an estimation thereof. Similarly, the operating conditions can include a measure of the change of position of the mixing valve with respect to a change in the actual mixed water temperature at the outlet.
By additionally considering the cold water inlet temperature, the control system only requires data relating to two other operating positions to characterise the external system.
The operating conditions may additionally include the temperature of the input hot water.
In this way, the control system only requires data relating to one intermediate position of the valve to characterise the external system.
Thus, by using the input cold and/or hot water temperatures, the control system is able to characterise the external system more quickly and easily.
Preferably the control system is continuously adaptive such that, should the properties of the external system change, the characterisation will also change. In other words, the applicable response or gain for the operating range will change. However, in addition, the control system may also determine the characterisation of the external water system with respect to time. In this way, the control system can predict conditions where the properties of the external water system change over time. For instance, the control system could compensate for the temperature of the hot water inlet decreasing over time as the temperature in a hot water supply tank decreases. Similarly, the control system could compensate for dead leg in supply pipes according to time since the mixing valve was last used and/or changes as the temperature of a supply pipe comes up to the temperature of the water it carries.
Preferably, upon stat up, the control system makes use of the characterisation to move the valve to a position predicted to produce the required temperature at the water outlet.
Indeed, according to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the inlets and outlets being for connection to an eternal water system;
a valve servo for moving the position of the valve; and
a control system for operating the valve servo and thereby controlling flow from the water outlet; wherein
the control system stores information relating position of the valve and valve servo to temperature at the outlet such that, upon start-up, when a desired temperature is selected the valve servo is initially operated to move the valve to the position stored for the selected temperature.
Where the control system uses a temperature sensor in the outlet together with a control loop, the control system positions the valve without using the control loop for a short predetermined period of time. In this way, when the control loop is again used, the valve position and the actual temperature should be close to the required position and temperature such that the required temperature can be reached more quickly and with less oscillation in temperature.
Often mixing valves will be used in systems which are shut down and restarted within a short period of time. For instance, in a domestic shower, the shower may be turned off briefly while the user is applying soap or shampoo.
Preferably, when the mixing valve is not used only for a very short period of time, the control system assumes that the conditions of the water system have not changed and jump starts a start up control loop to restore the valve to its position as previously used.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the inlets and outlets being for connection to an external water system;
a valve servo for moving the position of the valve; and
a control system for operating the valve servo and thereby controlling flow from the water outlet, wherein
when the mixing valve is not used only for a very short period of time, the control system assumes that the conditions of the external water system have not changed and jump starts a start-up control loop to restore the valve to its position as previously used.
In other words, irrespective of any other control systems or control loops, the valve may be driven directly to the position it had when it was last used.
In this way, the valve is moved directly to a position suitable for producing the desired outlet conditions. This is particularly useful for a mixing valve used to control both flow and temperature. Furthermore, by jump stating the start up control loop such that the control loop is at first ignored, the system avoids undue oscillations and time delay as the control loop brings he valve to its required position. The control loop may be activated once the valve has reached the required position.
In previous mixing valves for controlling the temperature of a water outlet, it was known to provide an intermediate maximum temperature stop so as to prevent use of the outlet above a preselected temperature. However, there is a problem that these stops can inadvertently be overridden.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for variably mixing hot and cold water;
a valve servo for moving the mixing valve;
a control system for operating the valve servo so as to provide a desired mixed water temperature; and
a control panel remote from the mixing valve and valve servo for providing a control signal to the control system to select the desired temperature; wherein
the control system includes a maximum temperature selector by which a user may specify a maximum mixed water temperature selectable by the control panel; and wherein
the control panel includes a display of selectable mixed water temperatures,
the display only showing temperatures up to the selected maximum mixed water temperature and
the display has a fixed predetermined extent, the scale of which is varied according to the selected maximum mixed water temperature.
In this way, users are only presented with available mixed water temperatures and, unlike previous systems where higher unselectable temperatures are displayed, no motivation is provided to select higher temperatures. Furthermore, the scale makes fill use of the available display and, furthermore, for low maximum temperatures, the scale can be increased to show changes in temperature with greater accuracy.
Preferably, the maximum temperature selector is provided proximate the mixing valve and the valve servo.
Since the control panel is provided remote from the mixing valve and the valve servo and since the maximum temperature selector is provided proximate the mixing valve and valve servo, it is not possible for a user to inadvertently change the temperature specified by the maximum temperature selector. Hence, a user may freely select temperatures using the control panel without any danger of selecting a temperature beyond that specified by the maximum temperature selector.
Despite this, by accessing the mixing valve and valve servo, it is still possible to provide a maximum temperature selector which easily adjusts the selected maximum temperature according to requirements.
The control panel may include a member movable between two predetermined end positions to select the mixed water temperature, one of the predetermined end positions selecting the selected maximum mixed water temperature and the scale of selectable mixed water temperatures between the two predetermined end positions being adjusted according to the selected maximum mixed water temperature.
In this way, for lower maximum temperatures, the full range of movement is still possible, such that temperatures may be selected with greater accuracy. This is applicable to sliders and also rotatable control knobs.
It should be noted that it would also be possible to provide a similar minimum temperature selector and to change the scales of the display and/or control member accordingly.
In previous systems where a flow of water is controlled by an electrically operable mixing valve, there has been a problem when power failures occur. In particular, without electrical power for the mixing valve, it remains in its open position. It has been proposed to provide mechanical actuators to allow the valve to be closed manually. However, these are inconvenient to use, particularly when the mixing valve is installed in a shower and, hence, the user is wet.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for controlling flow of water;
a valve servo for moving the mixing valve;
a control system for operating the valve servo to move the mix valve;
an electrical power input for receiving power for the valve servo and control system; and
an electrical energy store for powering tee valve servo and control system in the event that no power is received by the electrical power input, in such event, the control system operating the valve servo to move the valve to a position of no flow.
Hence, in the event of a power failure, the electrical energy store provides power to close the valve and shut off supply of water from the outlet.
This is particularly useful for valves having and preferably the apparatus has a valve member with apertures for hot and cold water and movable between a position of no flow and positions of mixed flow between maximum hot and maximum cold.
For these valves, a power failure may result also in changes in the external system providing the hot and cold water, such that the water outlet produces water which is unacceptably hot or cold. By means of the electrical energy store, it is possible safely to shut off the valve.
The valve member may provide a no flow position at two positions, one adjacent the maximum cold position and one adjacent the maximum hot position.
Although, in normal use, the valve member might be moved to the no flow position adjacent the maximum cold position, in the event that no power is received by the electrical power unit, the control system preferably operates the valve servo to move the valve member to the nearest of the two no flow positions.
In this way, the valve is moved to its off position most quickly and with the least amount of energy.
Preferably, in the event that no power is received by the electrical power unit, the control system switches off power to unnecessary components of the mixing valve apparatus so as to conserve power.
Thus, the control system only provides power to components essential for operating the mixing valve. For instance, any illumination of an associated control panel could be turned off.
In this way, depending on the size of the electrical energy store, it can be possible to continue operation of the mixing valve apparatus for some time before the valve servo moves the valve to a position of no flow.
In this respect, the control system could switch off power to any control loop for the valve on the basis that the operating conditions will not change over the short period of time following the power failure.
Preferably, the electrical energy store is a capacitor. This provides a longer service life than a battery and, also, allows energy storage at a higher voltage.
While power is received by the electrical power input, the capacitor may be charged to the highest possible safe voltage, for instance, at least 40 volts or a legislated maximum voltage, such as 42.4 volts.
In the event that no power is received by the electrical power input, the control system may determine the remaining electrical energy stored in the electrical energy store and operate the valve servo to move the valve to the position of no flow when the remaining electrical energy equals that needed to move the valve to the position of no flow.
In this way, for power failures of relatively short duration, it would be possible to continue operation of the mixing valve apparatus without interruption.
The valve servo may comprise a stepper motor. In this case, the control system preferably operates the stepper motor by half steps when power is received by the electrical power input and by whole steps in the event that no power is received by the electrical power input.
Preferably, in the event that no power is received by the electrical power input, the control system operates the valve servo to move the mixing valve to a position of no flow using the optimum servo trajectory resulting in the use of minimum power.
It will be appreciated that it is possible to operate a servo in many ways. In normal operation, the servo is usually operated to provide an optimum response by moving the valve quickly to a desired position Depending on the characteristics of the servo, it will also be possible to operate the servo in such a manner that it moves to a desired position with minimum use of power. By moving the mixing valve to a position of no flow using a minimum amount of power, the size of the electrical energy store may be minimised or the time during which the mixing valve apparatus may continue to operate during a power failure may be maximised.
In known electrically operated mixing valves, there is a problem of providing very accurate control of the mixing valve due to backlash in the gear train transferring motion to the mixing valve.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet;
a stepper motor;
a gear train for transferring motion of the stepper motor to the mixing valve;
a detector for detecting at least one predetermined position of the mixing valve; and
a control system for sequentially operating the stepper motor to move the mixing valve in one direction past said at least one predetermined position and in an opposite direction past said at least one predetermined position, thereby to determine with reference to the detector the back lash in the gear train.
In this way, when the control system is required to move the mixing valve in a direction opposite to the direction in which it was last moved, it can operate the stepper motor by an additional amount equal to the backlash in the gear train so as to move the mixing valve accurately to the required position. This can significantly improve the accuracy of the control system.
The control system is preferably responsive to a control signal to move the mixing valve to a position indicated by the control signal, the control system operating the stepper motor accordingly, taking account of the backlash in the gear train.
Thus the control signal could be derived from a temperature sensor in the water outlet for controlling the water outlet temperature. By correcting for the backlash in the gear train, it is then possible to move the mixing valve accurately as part of the control loop and make small changes in mixing valve position to more accurately control the outlet temperature.
Of course, the control signal may also be derived from a demand temperature input by a user.
In previous mixing valves, there has been a problem when the mixing valve is not operated for long periods of time. Due to stiction and such like between resilient seals and their sealing surfaces, undue strain can be placed on the valve servo and operating mechanism. Also additional wear and strain is placed on the resilient seals themselves.
According to the present invention, there is provided a mixing valve apparatus including:
a valve having at least one sealing surface against which at least one resilient seal presses;
a valve servo for moving the valve;
a control system for operating the valve servo in response to a control signal; wherein
in the absence of a control signal to move the valve within a predetermined period, the control system operates the valve automatically so as to keep the resilient seal from sticking to the sealing surface.
Preferably, the predetermined period is at least 24 hours. This is particularly useful for mixing valves used in showers. Showers are often used regularly at the same time each day. Hence, the control system will operate the valve servo if the shower is not operated by the user at this regular time.
Movement of the valve need only be sufficient to prevent the resilient seals from sticking to the sealing surfaces. Preferably, the valve is arranged such that it can be moved sufficiently to move the resilient seals relative to their sealing surfaces without the valve providing flow therethrough.
In this way, the external system in which the valve is installed will not be affected in any way by the operation.
Where a mixing valve is controlled by means of a control loop having a sensor in the outlet, it is often necessary to have a damped response. For example, where the control loop is used to maintain a particular temperature of water at the outlet, it is undesirable for the control loop to be undamped, since the system will unduly oscillate when moving to a new temperature and will overreact to changes in temperature resulting from minor changes to the inlet streams, for instance due to other usage on the same water supply. On the other hand, in certain circumstances, for instance a cold water supply failures it is extremely important that the system reacts quickly, for instance to shut off the water flow before a user becomes scalded.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the inlets and outlets being for connection to an external water system;
a valve servo for moving the position of the valve; and
a control system for operating the valve servo and thereby controlling flow from the water outlet, the control system including a temperature sensor for providing an indication of the temperature at the water outlet and a control loop for comparing the desired temperature with that provided by the temperature sensor so as to operate the valve servo; wherein
the control system additionally includes a transient detector for determining transients in the water flow from the temperature indicated by the temperature sensor and overriding the control loop to control the valve servo in the event of a transient.
In this way, during normal usage, the control loop may provide the desired damped response for controlling the outlet temperature. However, when a transient is detected by the transient detector, the control loop can be overridden so as to allow the control system to take immediate action in view of the detected temperature changes.
In other words, the normal control loop no longer has control over movement of the valve and the transient detector causes the valve to be moved rapidly to a safe position.
It will be appreciated that the effect of damping is often provided by the temperature sensor itself, since, for normal use, this need only have a relatively slow response time.
Preferably, in the event of a transient the valve servo is controlled to rapidly reduce the supply of water from the hot water inlet to the water outlet to substantially zero.
Preferably, the transient detector continuously monitors the rate of change in temperature indicated by the temperature sensor.
In this way, the transient detector may predict the actual temperature at the water outlet from the rate of change in temperature indicated by the temperature sensor and the time constant of the temperature sensor.
In other words, knowing the time constant of the temperature sensor and, hence, the limit to which it can show a rate of change in temperature, when the temperature sensor indicates a rate of change at that limit, the transient detector can predict an actual rate of change which is much greater.
In this way, the transient detector can predict an unacceptable rise in temperature such that the control system can take appropriate action.
Significant problems can arise with previous electronically controlled mixing valves due to faults in the system. For instance, failure of a temperature sensor can cause the mixing valve to be moved to a position producing an unacceptably high or low temperature.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the inlets and outlets being for connection to an external water system;
a valve servo for moving the position of the valve; and
a control system for operating the valve servo and thereby controlling flow from the water outlet; wherein
the control system includes an error detection circuit for detecting at least one of the following:
failure of a temperature sensor providing an indication of the temperature at the outlet;
failure of a selected intermediate maximum temperature for delivery from the outlet; and
disconnection of a control panel for controlling the control system.
In this way, the mixing valve apparatus is able to operate safely despite any faults which may occur.
Upon detecting an error, the control system can operate the mixing valve in a fail-safe mode, for instance moving the valve to full cold, to a safe intermediate temperature or shutting off the flow of water from the outlet.
Preferably, the error detection circuit only recognises indications of the temperature between predetermined limits as valid temperatures and determines failure of the temperature sensor when the indication temperature is outside the predetermined limits.
The temperature limits may be set such that if the temperature sensor goes open circuit or closed circuit, the error detection circuit determines an error. This prevents the control system driving the valve to full cold or full hot in response to an erroneous signal indicating maximum or minimum temperature.
The intermediate maximum temperature may be selected using a potentiometer, the maximum selectable intermediate maximum temperature being selected with the potentiometer at its maximum resistance and a fixed resistor being provided in series with the potentiometer such that higher resistances are detected as errors.
In this way, if the potentiometer for selecting the intermediate maximum temperature becomes disconnected, the open circuit is not recognised as a high intermediate maximum temperature and the control system takes appropriate action; for instance issuing a warning and shutting off the valve or using an internal default intermediate maximum temperature.
Preferably, the sum temperature selectable as the intermediate maximum temperature corresponds to a closed circuit such that an unwanted short circuit fails safe.
In particular, if a short circuit occurs, the system reacts to this as if the minimum temperature has been selected as the intermediate maximum temperature. Hence, such a failure will not cause scalding of the user.
Preferably, the error detection circuit regularly checks for valid signals from the control panel and detects an error when no valid signal is received.
For analogue control panels, the error detection circuit checks for valid signal levels, and, for digital control panels, the error detection circuit checks that the control panel can communicate.
In this way, should the control panel fail or become disconnected, the control system can take appropriate action, for instance shutting off the valve.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for mixing water from a cold water inlet and a hot water inlet and supplying the mixed water to a water outlet, the inlets and outlets being for connection to an external water system;
a valve servo for moving the position of the valve; and
a control system for operating the valve servo and thereby controlling flow from the water outlet; wherein
the control system stores information relating position of the valve and valve servo to temperature at the outlet such that, upon start-up, when a desired temperature is selected the valve servo is initially operated to move the valve to the position stored for the selected temperature.
According to the present invention, there is provided a mixing valve apparatus including:
a mixing valve for variably mixing hot and cold water;
a valve servo for moving the mixing valve;
a control system for connection to a remotely located control panel and for operating the valve servo so as to provide a desired mixed water temperature according to the control panel; wherein
the control system includes an input port suitable for connection selectively to an analogue control panel and a digital control panel.
Preferably, the input port includes six lines of which two lines are suitable for analog control signals.
Preferably the input port includes an input termination circuit.
Preferably the input termination circuit includes;
a first capacitor between ground and an input port;
a first resistor between the input port and a digital input;
a second resistor between the input port and au analog input; and
a second capacitor between the analog input and ground; wherein
the second resistor has a higher impedance with respect to the first resistor.
According to the present invention, there is provided a method of communicating with a mixing valve apparatus having a mixing valve for variably mixing hot and cold water, a valve servo for moving the mixing valve and a control system with a digital interface allowing input of a digital signal so as to cause the control system to operate the valve servo and provide a desired nixed water temperature, the method comprising:
providing a control message of 8 bits having, in order, a destination address byte, a source address byte, a command number byte, three payload bytes and two CRC bytes.
Preferably, the command number has at least six values representing respectively report system status, switch valve on or off, set temperature, switch pump on or off, report temperature and report pump status.
It should be noted that any of the features discussed above can be combined together in any combination in a water mixing valve apparatus so as to give rise to a mixing valve apparatus having the corresponding advantages.